Morphology of radioactive ⁵⁶Ni-rich matter produced by explosive burning in shock-heated ejecta. The snapshots display isosurfaces where the mass fraction of ⁵⁶Ni plus the neutron-rich tracer nucleus equals 3%. The isosurfaces are shown for four 3D models at two different epochs: shortly before the SN shock crosses the (C+O)/He composition interface in the progenitor star (upper row), and long after the shock breakout (lower row). In the top left corner of each panel, we give the name of the model and the post-bounce time of the snapshot. The colors give the radial velocity on the isosurface, and the color-coding is defined at the bottom of each panel. The size of the displayed volume and of the clumps can be estimated from the yardsticks given in the lower left corner of each panel. There is a striking difference between model B15-2 and the other three models in the final morphology of the ⁵⁶Ni-rich ejecta, which arises from their specific progenitor structures and the influence of the latter on the unsteady SN shock propagation.